Herein, a domestic animal is defined as an animal being purposely selected, or having been derived from an animal having been purposely selected, for having desired genotypic or potential phenotypic properties.
Domestic animals provide a rich resource of genetic and phenotypic variation; traditionally, domestication involves selecting an animal or its offspring for having desired genotypic or potential phenotypic properties. This selection process has in the past century been facilitated by growing understanding and utilization of the laws of Mendelian inheritance. One of the major problems in breeding programs of domestic animals is the negative genetic correlation between reproductive capacity and production traits. This is, for example, the case in cattle (a high milk production generally results in slim cows and bulls), poultry (broiler lines have a low level of egg production and layers have generally very low muscle growth), pigs (very prolific sows are, in general, fat and have comparatively less meat), or sheep (high prolific breeds have low carcass quality and vice versa). PCT International Patent Application WO 00/36143 provides a method for selecting an animal for having desired genotypic or potential phenotypic properties comprising testing the animal for the presence of a parentally imprinted qualitative or quantitative trait locus (QTL). Knowledge of the parental imprinting character of various traits allows selection of, for example, sire lines homozygous for a paternally imprinted QTL, for example, linked with muscle production or growth; the selection for such traits can thus be less stringent in dam lines in favor of the reproductive quality.
The phenomenon of genetic or parental imprinting has earlier never been utilized in selecting domestic animals; it was never considered feasible to employ this elusive genetic characteristic in practical breeding programs. A breeding program, wherein knowledge of the parental imprinting character of a desired trait, as demonstrated herein is utilized, increases the accuracy of the breeding value estimation and speeds up selection compared to conventional breeding programs. For example, selecting genes characterized by paternal imprinting is provided to help increase uniformity; a (terminal) parent homozygous for the “good or wanted” alleles will pass them to all offspring, regardless of the other parent's alleles, and the offspring will all express the desired parent's alleles. This results in more uniform offspring. Alleles that are interesting or favorable from the maternal side are often the ones that have opposite effects to alleles from the paternal side. For example, in meat animals such as pigs, alleles linked with meat or carcass quality traits such as intramuscular fat or muscle mass could be fixed in the dam lines while alleles linked with reduced back fat could be fixed in the sire lines. Other desirable combinations are, for example, fertility, teat number and/or milk yield in the female line with increased growth rates, reduced back fat and/or increased muscle mass in the male lines.
The purpose of breeding programs in livestock is to enhance the performances of animals by improving their genetic composition. In essence, this improvement accrues by increasing the frequency of the most favorable alleles for the genes influencing the performance characteristics of interest. These genes are referred to as QTL. Until the beginning of the nineties, genetic improvement was achieved via the use of biometrical methods, but without molecular knowledge of the underlying QTL. Now, the identification of causative mutations for Quantitative Trait Loci (QTLs) is a major hurdle in genetic studies of multifactorial traits and disorders. The imprinted IGF2-linked QTL is one of the major porcine QTLs for body composition. It was first identified in intercrosses between the European Wild Boar and Large White domestic pigs and between Piétrain and Large White pigs.(1, 2) The data showed that alleles from the Large White and Piétrain breed, respectively, were associated with increased muscle mass and reduced back-fat thickness, consistent with the existing breed differences in the two crosses. A paternally expressed IGF2-linked QTL was subsequently documented in intercrosses between Chinese Meishan and Large White/Landrace pigs(3) and between Berkshire and Large White pigs.(4) In both cases, the allele for high muscle mass was inherited from the lean Large White/Landrace breed. However, there are a large number of potentially important elements that may influence IGF2 function. Recent sequence analysis (Amarger et al. 2002) provided a partial sequence of the INS-IGF2-H19 region and revealed as many as 97 conserved elements between human and pig.